Apparatus for amplifying electromagnetic signal-waves.



No. 7|4,832. Patented Dec. 2, I902.

J. S. STONE.

-APP ARITU S FOR AMPLIFYING ELEGTROMAGNE'HC SIGNAL WAVES.

LApplication filed Jim. 23, 1901.1

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lilivrrn S ratus TE T QEEIQE- JOHN STONE STONE, OF BOSTON,MASSACHUSETTS, ASSIGNOR TO LOUIS E. TVIIIOHER, ALEXANDER P. BROVVNE, ANDBRAINERD T. JUDKINS,

TRUSTEES.

APPARATUS FOR AMPLlFYlNG ELECTROMAGNETIC SIGNAL-WAVES.

SPECIFICATION forming part of Letters Patent No. 714,832, dated December2, 1902; Application filed January 23, 1901. Serial No. 44,389. (Nomodel.)

To atZZ whom, it may concern:

Be it known that I, JOHN STONE STONE, a citizen of the United States,residing at Boston, in the county of Suffolk and State of Massachusetts,have invented certain new and useful Improvements in Apparatus forAmplifying Electromagnetic Signal-TVaves, of which the following is aspecification.

The invention relates to the art of wireless or space telegraphy, andmore particularly to that form of space telegraphy in which the signalsemanate from an elevated conductor in the form of electromagnetic waves.Such systems shall hereinafter be designated as elevated-conductorsystems of space telegraphy.

Heretofore, as far as I am aware, in elevated-conductor systems of spacetelegra'phy the electromagnetic waves emanating from the elevatedconductor have either been of such moderate frequency as thosecorresponding to audible sound-waves or of such enormously-greaterfrequencies as can at present only be obtained by the discharge ofelectric condensers through circuits possessing inductance. Thehigh-frequency waves have certain advantages over the comparatively lowfrequency waves for the purposes of elevated-conductor systems of spacetelegraphy; but whereas heretofore in the elevated-conductor systems ofspace telegraphy employing low frequencies the electrical oscillationsin the elevated conductor are conveyed to it from a primary circuit bymeans of a step-up transformer, thereby greatly amplifying the amplitudeof the vibrations conveyed to the elevated conductor, it has, so far asI am aware, heretofore been exclusively the practice in high-frequencyelevated-conductor systems of space telegraphy to'develop the electricaloscillations in the elevated conductor by causing an oscillatorydischarge to take place at a spark-gap in the elevated conductor itself.This method of developing the electric oscillations directly in thevertical conductor presents the disadvantage of limiting the amplitudeof the resulting oscillations to a potential difference just sufficientto produce a spark at the spark-gap in the ele vated conductor.

The object of the present invention is to overcome in the high-frequencyelevated-conductor system of space telegraphy the defect described abovewhereby the amplitude of the electric oscillations in the elevatedconductor is limited to the potential difference required to produce aspark at the spark-gap contained in the elevated conductor. This objectIattain by developing the high-frequency oscillations required for thepurposes of high-frequency space telegraphy in a primary circuit by thecharge and discharge of an electric condenser and then causing theseoscillations by means of astep-up transformer to produce inductivelycorresponding oscillations of increased amplitude in the elevatedconductor, the amplitude of these oscillations being through theintermediary of the stepup transformer much amplified.

In my application filed January 23, 1901, Serial No. 44,384, forimprovement in apparatus for selective electric signaling I havedisclosed the herein-described apparatus for amplifying electromagneticsignal-waves and have therein illustrated the same embodiment of thisinvention as here disclosed, but have not therein claimed this apparatusbroadly.

An embodiment of this invention is depicted in the drawing whichaccompanies and forms a part of this specification.

The figure is a diagram illustrating an organization of circuits andapparatus for producing electrical oscillations of great amplitude in anelevated conductor.

In the diagram, a is a generator of current of a relatively moderatefrequency.

7a is a key by means of which the operation of the apparatus as a wholemay be controlled and whereby oscillations may be developed or not in anelevated conductor at the will of the operator.

M is an induction-coil or step-up transformer,whose primary andsecondary are designated as N and N respectively.

S is a spark-gap.

O is a condenser.

M is a second step-up transformer, whose primary and secondary aredesignated by N and N,, respectively.

The elevated conductor V is grounded at the earth connection E.

The operation of the apparatusis as follows: When set in motion in anysuitable manner, the generator at develops an alternating, electromotiveforce of relatively moderate frequency, which when the key is depresseddevelops a current in the primary circuit d 74: N. This current inducesa very high potential alternating electromotive force in the secondarycoil N which tends to alternately charge the condenser (J to a highpotential first in one direction and then in the other; but thespark-gap S is so adjusted that when the condenser is charged almost toits maximum in either direction a spark passes at S, and the condenseris thereby permitted to discharge through the circuit S N C. Thisdischarge is oscillatoryin character, owing to the inductance of thecoil N or to the inductance of an auxiliary coil (shown in the drawingat L) which is introduced in the circuit S N O for the purpose ofcontrolling the frequency of the resultingvibrations. This coilis shownin my application hereinbefore referred to, and its function indetermining a simple harmonic wave is therein fully described. Thevibrations in the primary N induce vibrations of much greater amplitudein the secondary conductor V N E, and these latter give rise toelectromagnetic waves whose am plitude and frequency correspond to theamplitude and frequency of the electric oscilla tions. In this mannerelectromagnetic waves are caused to emanate from the vertical conductorwhich are of greater amplitude than it would be possible to produce froma corresponding elevated conductor in which the electric oscillationsare produced by charging the conductor to a high potential and thenpermitting the conductor to discharge to earth. By manipulating the keyIt in accordance with a predetermined code telegraphic messages may betransmitted from the elevated conductor by electromagnetic wavesemanating therefrom, and the messages so transmitted may be received byany suitable elevated-conductor space-telegraph receiver within therange of influence of the transmitting elevated conductor V.

Certain precautions must be taken in the construction of the coil M inorder to overcome the effects of dielectric and magnetic hysteresis andthe effects of capacity and conductance leakage between the variousconvolutions of the coil; but these precautions are no different fromthose which have long been recognized as necessary in the constructionof inductance-coils to be used in high-frequency circuits. For a givendielectric medium the conditions governing conductive and inductive orcapacity leakage are practically identical. The wire must be ofrelatively small diameter, and the distance separating two convolutionsbetween which a considerable diiference of potential exists during theoperation of the apparatus should be relatively large. For this purposeflat spirals have been employed; but any other convenient form may beemployed, provided such proportions are taken as will sufficientlydiminish the electrostatic capacity of the convolutions between whichhigh differences of potential occur during the operation of theapparatus. The necessityof avoiding dielectric and magnetic hysteresismakes it necessary to avoid as much as possible the use of solid andliquid dielectric having great dielectric hysteresis and also imposesthe condition that no iron shall be placed in or about the coils exceptit be so placed as to have but slight induction developed in it by thecurrent in the coil.

As soon as the spark-gap S has been broken down the greatest differencesof potential in the circuit S O N occur at the condenser O, and it isthere that the displacement-current is greatest. For this reason it isnecessary to so construct the condenser C that there shall be a minimumof dielectric hysteresis. This may be most easily accomplished by usingan air-condenser. Though it is possible that some other dielectric,either solid or liquid, may be found to be sufficiently free fromdielectric hysteresis, yet, so far as my experience extends, air is thepreferred dielectric to employ in the condenser. When the circuit S O Nis supporting the oscillating discharge of the condenser C, the greatestmagnetization occurs in the said coil N or in the hereinbefore-mentionedauxiliary coil employed to control the frequency of the oscillations.For this reason it is necessary to so construct the coil N and theauxiliary coil as to minimize the magnetic hysteresis in them. Thisresult may be accomplished by excluding iron or other paramagneticmaterials from these coils and from their immediate neightoo borhood.Though it may be possible to employ finely-divided soft iron embedded ina dielectric matrix to enhance the magnetization in these coils, I amnot prepared to recommend the use of such material as a core for thecoils, and, so far as my experience extends, coils from the constructionof which all paramagnetic material is excluded are the preferred coilsto employ in the circuit S O N. Though the displacement-currents aregreatest at the condenser, there is nevertheless, as hereinbeforestated, inductive or capacity leakage between the turns of the coili.6., displacement-currents flow between the convolutions of the coil, andthese displacementcurrents, as well as the hysteretic losses which theymay involve, should be minimized in the manner hereinbefore described;but it is not necessary to indefinitely diminish thesedisplacement-currents, and it is sufficient to so design the coils thatthey shall behave for on rrents ofthe frequency used practically like aconductor having a fixed inductance and a fixed resistance, but devoidof appreciable capacity. Coils constructed in the usual way do notbehave for high frequencies as if they had a fixed resistance andinductance and no capacity, but partake more of the character ofconductors having distributed resistance, inductance, and capacity. Infact, they may in some instances behave with high frequencies more likecondensers than like conductors having fixed resistance and inductanceand no capacity. Since a coil constructed in the usual way behaves forhigh frequencies as a conductor having distributed resistance,inductance, and capacity, it follows that such a coil will show for highfrequencies the same quasi-resonance as is observed with low frequenciesinlong aerial lines and cables 6. e., that it will per se and withoutthe intermediary of a condenser show a slight degree of selectivity forsome particular frequency and for certain multiples of that frequency,just as a stretched string which has distributed inertia and elasticitywill respond to a particular tone, calledits fundamental, and to allother tones whose periods are aliquot parts of the periods of thatfundamental; but it is not with such quasi-resonance that the presentinvention is carried into effect. A general criterion which determinesthe utility of a coil for tuning a circuit toa particular high frequencyis that the potential energy of the displacement-currents in the coilshall be small compared to the kinetic energy of theconduction-currentflowing through the coil when the coil is traversed bya currentof that frequency. I have found that for a singlelayer coil thefollowing procedure is sufficient for practical purposes: Determine theinductance of the coil by formulae to be found in the textbooks andtreatises on electricity and magnetism. This will enable the kineticenergy of the coil to be determined for any particular current and willalso permit of the determination of what would be the potential gradientalong the coil for the current of the frequency to be employed if thecoil were devoid of distributed electrostatic capacity.

Next calculate the electrostatic capacity between an end turn and eachof the remaining turns of the coil. These capacities, together with thepotential gradient found, will enable the potential energy to bedetermined, and if the ratio of the potential energy to the kineticenergy so found be negligible compared to unity the coil willpracticallysatisfy the requirements hereinbefore mentioned. If the coildoes not meet the requirements, the design should be so changed as toincrease the separation between the turns, or the size of the wireshould be diminished or the dimensions of the coil so otherwise alteredas to decrease the distributed capacity without proportionatelydiminishingtheinductance. Thecalculations may be greatly abbreviated andthe liability to error greatly reduced if the results of thecomputations be plotted in curves. Regarding the effect of a dielectriccore in a coil to be used for tuning a circuit to a high frequency, itis sufficient to state that the preferred form of support for such acoil is any skeleton frame which will hold the turns of wire in placewithout exposing much surface of contact to the wires and affording aminimum of opportunity for the development of displacementcurrentswithin itself. This form of skeleton frame is well known in the art,having been fully described in Vol. 49 (19001901) of the Journal oftheSociety ofArlzs, London, in the report of a lecture by Prof. J. A.Fleming. It is by no means necessary to use this support; but I find ita convenientmeans for accomplishing the aforesaid result.

The injunctions hereinbefore given regarding the construction of thecoils to be employed in circuit S C N apply with equal force to both thecoil M and the auxiliary coil used to control the frequency of theoscillations in this resonant circuit; but the coil N may be made toperform the function of the auxiliary coil and control the frequency ofthe oscillations or, what amounts to the same thing, the auxiliary coilmay be made a part of the coilN, Which then performs both functions- 2'.e., of controlling the frequency of the 0scillations and of impressingthese oscillations upon the elevated conductor. This double function maybe performed by the coil N if it be so designed that its self-inductionis made large compared to the ratio of the mutual induction byinductance of the secondary. This simply means that the inductance ofthe auxiliary coil must be added to the inductance of N withoutappreciably increasing the mutual inductance between that coil and thesecondary coilN' The performance of the apparatus is the same whetherthe auxiliary inductance necessary to control the frequency of theoscillations be located in a separate coil or incorporated in the coil Nof the transformer M, though it will be found in practice moreconvenient to locate the auxiliary inductance in a separate coil, owingto the greater complexity of the numerical calculations which have to bemade when the auxiliary inductance is to be furnished by the coil N.

I am aware of Patents Nos. 645,576 and 649,621 to Nikola Tesla, whichdisclose a method and apparatus for impressing on an aerial conductoroscillations of high frequency by means of a transformer; but in saidpatents no means are disclosed for producing simple harmonic waves, and,furthermore, as the system therein disclosed is for the transmission ofelectrical energy by conduction through a rarefied atmosphere a simpleharmonic wave is not necessary; but as I am the first to discover theutility of a simple harmonic wave in the transmission of intelligence byelectromagnetic waves by the systemdisclosed in my application aforesaidand am the first to discover the means for producing said wave formeffectivelyI claim the same herein broadly.

It is to be definitely understand that the present invention is notconfined to the special form of apparatus shown and described in thisspecification as means of developing simple harmonic electric vibrationsin the primary circuit of the coil M, any suitable means of developingsimple harmonic electric vibrations in the primary of the coil M beingconsistent With the invention.

What I claim is 1. In an apparatus for producing high-frequency simpleharmonic electromagnetic signal-Waves, means of developing simpleharmonic electric oscillations of high frequency in a primary circuit,an elevated conductor I and a step-up transformer having its primary

